Adsorptive performance of bismuth-doped Ni-Zn-Co ferrite nanoparticles for the removal of methylene blue dye.

Cancer, kidney and liver damage, and even death result from water contaminated with textile dyes. This study highlighted a key approach for treating water contaminated with methylene blue (MB) dye. Bismuth-doped ferrite nanoparticles (NiZnCoBiFeO) with 0 ≤  ×  ≤ 0.2 were synthesized using a chemical co-precipitation technique. For the structural analysis, X-ray diffraction (XRD) confirmed the successful formation of ferrite nanoparticles with a hematite phase of 21.02% for x = 0.2. The crystallite size decreased from 30.12 to 13.65 nm, as x increased from 0 to 0.2. Also, a decrease in the grain size from 24.57 to 12.37 nm was verified via transmission electron microscope (TEM) analysis. Furthermore, the X-ray photoelectron spectroscopy (XPS) confirmed the optimal stoichiometric proportions of the synthesized nanoparticles through the elemental composition analyzed. Additionally, XPS analysis revealed that the un-doped sample has gained the highest number of defects along with the photoluminescence spectra (PL) discussion. The optical analysis was investigated by photoluminescence spectra (PL) through several excitation wavelengths. The detected PL peaks in the near-band energy and the defect-level emission region confirmed the recombination rate and the presence of defects, respectively. Doping ferrite nanoparticles with bismuth increased the specific surface area from 43.82 to 71.83 m·g and altered pore volume and diameter. For further investigation, the adsorption performance of ferrite nanoparticles was tested using MB as a pollutant. Un-doped nanoparticles demonstrated significant adsorption activity, removing 97.1% of MB after a contact time of 120 min. Furthermore, un-doped nanoparticles exhibited improved adsorption activity in a basic medium, while Bi-doped nanoparticles showed enhanced performance in an acidic medium. This result was due to Bi-doping altering the surface charge, as confirmed by zeta potential analysis. Among the applied non-linear isotherms, the Freundlich model best described the adsorption of MB onto the NiZnCoBiFeO nanoparticles. Increasing the temperature boosted the adsorption of MB onto the prepared nanoparticles.